In wireless networks the radio frequency (RF) coverage of base stations to subscriber stations can be impaired by a shielded space or blocked shadow areas, e.g., an underground shopping mall, a tunnel, an underground parking lot, etc. In the shadowed areas installation of a base station may not be economically or technically feasible.
An RF repeater enables service in a blind or shadowed zone by receiving a signal outside of the shadowed area at a Donor antenna and performing low-noise amplification and then reradiating the signal through a Server antenna to into the RF coverage gap. The RF repeater is interposed between a base station and a mobile terminal to improve a downlink radio signal received from the base station to the mobile terminal, and an uplink radio signal from the terminal to the base station. The repeater improves poor RF performance due to obstructions between the base station and the terminal without requiring additional base station hardware.
In deploying an RF repeater isolation between a transmit (TX) antenna and an receive (RX) antenna is required to minimize the possibility of the RX antenna receiving feedback from the TX antenna. Accordingly, upon the installation the isolation status between the antennas must be accounted for. In particular, since a time division duplex—orthogonal frequency division multiplexing/orthogonal frequency division multiple access (TDD-OFDM/OFDMA) repeaters utilizes the same frequency both the downlink antenna direction and the uplink antenna direction, the distance and direction between the antennas must be well selected in order to ensure sufficient isolation is achieved.
A conventional RF repeater and the peripheral devices start micro oscillation when a gain of the RF repeater is sufficiently increased above an isolation status value since any output is not detected in the uplink when the downlink is shut off. At this time, since a value detected in an uplink output terminal is represented as an oscillation output by the isolation, testing the isolation status by using the value has been adopted during installation of repeaters. Since the isolation testing is performed during installation any subsequent changes in the RF environment can result in oscillation and degradation of service. Service to the repeater is then required to determine the isolation status which utilizes technical resources to go to the repeater and physically test the link. While service degradation occurs network performance is decreased and operational costs are increased in having to service the repeater.
Accordingly, apparatus and methods that enable ease of isolation measurement and self-oscillations prevention remains highly desirable.